One of the problems encountered in the fabrication of plastic parts, or parts fabricated from other similarly suitable materials, in a compression molding process is the periodic failure of parts to be successfully ejected from the mold cavity upon completion of the mold machine cycle. Clearly, retention of molded parts in the cavity will result in subsequent unsatisfactorally molded parts.
In the past this problem has been addressed simply by having an operator monitor the molding process and turn the mold press off upon observation of a non-ejected part. However, because an operator could be expected on occasion to fail to observe non-ejected part and because, in any event, this approach introduced undesirable delay and attendant expense into the molding process, an improved solution was sought.
Some limitations inherent in the operator-monitor approach can be circumvented by the installation of a miniature lamp in the mold machine. In a manner roughly analogous to the one described below, the lamps can be used to detect the retention of a molded part in the mold cavity and to appropriately modify the operation of the mold machine. However, initial installation of miniature lamps has proved costly and the expense of installation is exacerbated by the relatively short lamp life resulting from the hostile environment, that is, heat and vibration, presented by the molding process.